Pulse oximetry is a widely accepted noninvasive procedure for measuring the oxygen saturation level of arterial blood, an indicator of a person's oxygen supply. Early detection of low blood oxygen level is critical in the medical field, for example in critical care and surgical applications, because an insufficient supply of oxygen can result in brain damage and death in a matter of minutes. FIG. 1 illustrates a pulse oximetry system 100 having a sensor 110 applied to a patient, a monitor 160 and a patient cable 140 connecting the sensor 110 and the monitor 160. The sensor 110 is attached to a tissue site, such as an adult patient's finger (as shown). Other sensor types are configured to attach, say, to a neonatal patient's foot. The sensor 110 is configured with both red and infrared LEDs 112 (hidden) that, for finger attachment, project light through the fingernail and into the blood vessels and capillaries underneath. A photodiode 114 (not visible) is positioned at the finger tip opposite the fingernail so as to detect the LED emitted light as it emerges from the finger tissues.